# Forum Home Renovation Flooring  how to fill gaps in between floorboards

## wajor

Hi All, 
I have a t&G jarrah floor that has quite a few gaps in between boards. I want to sand these back and re seal. Does anyone know of a product tofill these gaps (2-3mm) prior to applying Traffic urethane? 
Thanks for any advice 
Wayne

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## SilentButDeadly

http://www.timbermate.com.au/products/timbermate.html

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## Vernonv

I think if you fill it with anything that isn't flexible, it will eventually crack, dislodge and look crappy.

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## wajor

Thats what I was worried about using the Timbermate (I have used that for filling the nail holes). Hopefully someone may know of something else.  
Thanks so far, 
Wayne

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## Gooner

I used timbermate on my floorboards before finishing. It's only been about 15 months and there are fine movement cracks in many of the areas I filled. It doesn;t look too bad as they are fine cracks, but cracked none the less. 
Timbermate is very often recommended for this job on these forums (which is why I used it) but I do not think it suitable.

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## TimDavis

As a floorsander this is the most commonly asked question of all. The simple fact of the matter is that there is no suitable product for filling gaps in boards. Hard fillers crack and fall out, flexible fillers are likely to be squeezed out when the boards expand. Believe me I have tried eveything. A timber floor of any size is a vast expanse of wood that will be forever moving from side to side (more so than laterally). Filling the gaps is not and has never been a recommended practice despite more recent trends, and claims by product manufacturers like Timbermate that it works. In short, it doesn't. Look at almost any old timber floor and you will find gaps, it's what wood and wooden floors do, move constantly with atmospheric moisture variations. Learn to live with it and accept that wood is a natural product and is never truly stable.
The only method I believe may work, although I've only read about it is to cut narrow slivers of similar timber and pack the gaps using a good adhesive. However if the boards contract further another gap will open. If the boards expand you may well have serious problems when the expansion gap around the room perimeter is taken up and either the boards buckle or start pushing wall frames, not a nice proposition.
Filling  gaps is just a "stop gap" measure which may work for some time but will ultimately fail, despite what many people claim.

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## UteMad

Sika 290 dc ... ring sika its made for this purpose for marine applications.. have done it before for a customer who had 8mm wide gaps in places from old recycled boards layed poorly.. also when we did heritage stuff for rocks authority 
do before sanding its way easier than the way i had to do it with masking tape both sides 
cheers utemad

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## glock40sw

> Sika 290 dc ... ring sika its made for this purpose for marine applications.. have done it before for a customer who had 8mm wide gaps in places from old recycled boards layed poorly.. also when we did heritage stuff for rocks authority 
> do before sanding its way easier than the way i had to do it with masking tape both sides 
> cheers utemad

  
WHat He said..... :2thumbsup:

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## TimDavis

I still stand by my claim. ANY filler will ultimately fail. I have lived on the Gippsland Lakes all my life and worked on, travelled on and seen, hundreds of old boats (and a few wooden floors too). Even Sikaflex, as good a product as it is will not withstand an expanding deck or floorboard, it is still only a temporary solution. On boat decks exposure levels are admittedly higher than an interior floor, but I have never seen any filler last more than a few years on a boat, and not much longer on a floor. It all falls out sooner or later.
If people insist on filling floorboard gaps Sikaflex is probably capable of withstanding more movement than most products but it is expensive and still only temporary. On a boat re "caulking" a deck is a regular maintenance item, no difference on a floor.

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## konmanos

Guys, after reviewing this thread and having the same / similar issue - gaps in my floorboards - where the tongue of the T&G was broken away in sections - and I was having drafts come in from under the house - I tried SikaFlex 290DC (black).... Apply very carefully in the gaps (make sure that the gaps are clean and free from any debris), make sure you have spatula and metho handy as you will want to have clean lines - of where the Sikaflex is only in the gaps and not on the floorboard. When you have applied the sikaflex - then with the wet Spatula (metho) - scrape along the gap (wither side of floorboards) and it will push the sikaflex further into the gap as well as smoothing off the top. To remove Sikaflex from the floorboards - use a clean rag with metho - as Sikaflex - tends to stain - so keep rubbing and it will come off - make sure the rag is clean.... Very good product !! and very flexible - where moving boards are in place.

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## seriph1

For anyone with a period home and who can actually get under their house (we can't which is a total pain) I recommend insulation  -  it stops the drafts in their tracks while retaining the great appeal of the old floors. There are a number of products out there to choose from. The alternative we are probably going to opt for is to seal the perimeter of our home with cement sheet and add a couple of vents to prevent mould. This greatly restricts the air movement under the home therefore the drafts will be mostly eradicated. It is also cheaper than insulating in between the joists.

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## Dusty

Filling gaps in floorboards. What a pain in the neck. 
The truth is, over time, a timber floor will move as everyone has already mentioned.  The main point is how much will it move? And how badly will it affect the filler? Who cares it's not my house. This might sound callous, but it's the attitude we flooring contractors have to carry with us if we are to fill the gaps in someone's home. 
I'm one of the very few floor sanders I know who doesn't have a problem with filling the gaps. My take on the issue is this.... 
Of course, some of the putty will crack. And, of course, some of it will fall out. 
But how much will come out? Well from my experience, if the filling is done as well as you can expect it to be done I'm reckoning that, maybe, less than 4% of what gets packed into the gaps comes out. 4 or, maybe 5%. In my book that's bugger all and quite acceptable. I can live with that. 
Now, from my experience, Timbermate is the finest putty to be used in this sort of application. 
The biggest problem is not the natural movement of the boards after the floor is finished, the biggest problem is the flooring contractor putting the filler in the gaps. How hard did he push the putty in? How much care and effort has been shown? At what stage of the sanding & finishing process did the filling get done? All this can have a major impact on just how well this gap filling is going to hold up. 
In the past, as I was taught, we often used to punch a floor, then, maybe, do a rough sand and start filling. After the floor was filled we would start to do some of the finer sanding. 
This is where the problems start. Even though the floor has been punched, many nails will, once again, be uncovered and require re-punching. Now, imagine for a second what happens to all that putty you've just put in to the floor as soon as you start banging in a couple of nails - Yep, the filler vibrates lose with every strike of the hammer on the punch. Along with that, we also have to contend with the vibrations caused from the big sanding machine vibrating the b'jesus out of the floor.  Again, loosening even more putty. 
So , I changed completely the order in which I do things to give the putty every possible chance of staying put. And, I'm pleased to report that I'm having great success. 
Here's what I do now. I make sure _each_ & _every_ nail has been punched before attempting to put in any filler. I do all of my heavy sanding with the main machine before putting any putty in the floor. I sand the floor to a fine finish before putting any filler in the floor. All of this ensures that once that filler is packed, nothing I do is gonna bang it back out again. Once the floor has been filled, I do a final light sand with a rotary machine which buffs off the excess filler and leaves the floor with a 'Super Fine' finish ready for coating. 
Since adopting the above routine, I've had nothing but excellent results with both putting the filler in and how well put it remains. 
To mix up the Timbermate ready to pack into the gaps, I use a cake mixer and add just a little water at a time until the filler is about the consistency of toothpaste. As it's being packed in the filler begins to dry out as you're working it. These dried out bits are put into another container ready to be mixed again with the beater. Well that's it really. 
Just to stress the point. Make sure all the heavy banging and sanding is done before attempting to commence the filling and you should be right. 
Below are some photo's from a job I did a couple of months back inwhich the owner had already had the floor polished and the contractor told them the gaps couldn't be filled. In one of the photo's the only bit I didn't fill is where the dishwwasher is to go. This clearly shows the difference between a filled and un-filled bit of flooring. You can also see that it's well worth the effort to fill it, and to fill it right.  
Also, HERE is a link to a page on my own web-site showing another floor that had a massive amount of filling done to it, in the same manner as I've described above.  
The Photo's.

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## Gooner

Good post Dusty. 
One thing I have noticed is that when I did my floorboards I spent a lot of time researching the correct process and products. Most of the books and video instructions were U.S. based. I noticed that in virtually all of them, the method used to fill the gaps was to prepare a big batch of liquid filler and simply pour and spread it across the entire floor using a broom/brush or squeegee. It seemed that this was a standard practice in the floor preparation stage. 
However, it seems this is not done at all within Australia. Any reason why? Surely we have access to the same products?

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## Dusty

G'day Paul.
In the States Timbermate is the putty of choice for most contractors. Which is tremendous for an Australian product. 
Unfortunately, what you've touched on is one of the big problems with the filling of gaps and that's what I'm trying to allude to in the previous post. It's more to do with the actual application of the filler causing problems, rather than the filler it's self being at fault. 
When you see a video showing someone sweeping, or spreading the putty in with a squeeze the first thing it tells you is that the putty must be pretty damn runny. And, if it's pretty damn runny it stands to reason that the runny putty will dry out - considerably. And, that is the big problem. Once the moisture has gone out of it (and it needs a fair bit of water to make it that thin) the putty will sink, shrink and crack.  
Along with that, because the putty was so full of moisture to make it _that_ runny it also stands to reason that the edges of the boards will take in water and therefore swell themselves. Once the boards dry out and shrink back to their original size it only adds to the problem of the putty failing. 
So, back to what I was saying earlier. I only mix the putty to the thickness of toothpaste, which is smooth enough to be packed into a the gaps, but not wet, or runny enough to cause too much grief. I pack the putty in painstakingly with a flat blade putty knife. There is no way the mixture I'm using could be broomed in, or the like, it's just simply way to dense. 
Anyhow, I've added a few more photo's, this time showing the actual filling process.

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## TimDavis

Dusty, I agree with your technique but with one variation. Whenever I trowel fill with timbermate I don't fill untill after the first coat. This way the timber is sealed, with luck even down into the gaps too, preventing the boards sucking up moisture. I then polyvac with 80 grit and rub the edges by hand, the excess filler comes off very easily. I then run the polyvac around again with 150-180 grit to take out any 80 grit swirly marks and whack the second and final coats on ( after appropriate preparation). Hey presto, floor is filled, filler's got two coats over the top to help it stay in place and the job looks good, until 5 percent of the filler falls out. I warn the owner about this and hope most of it stays put. Never had any call backs yet, but still only reluctantly fill gaps.

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## Dusty

I've done it that way in the past, particularly when I worked on my own.  But now with my son well into his second year of work, and one of his mates coming in part time, I find it's the best way to utilize their time. And because the floor is fully filled before the coat goes down it means I can quickly roll the second coat on without any mucking around and get us to the next job, or, _even better_ an early day. Which is pretty important, in my book. :2thumbsup:  
Quick edit:
I only fill floors if I'm requested to do so. It's not something we do on every job. Thankfully.

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## jags

Hi Wayne 
I was in the same position as you are now about two year ago .
I had a number of gaps in my floor , 85mm jarrah boards and after the great advise i got from the pro's on this site i desided not to fill the gaps . As what i understood in short from what everyone said was it could be done but it would not last . 
I think it depends on the style of the interior you are going for .As to weather it is worth doing .
My house is a classic style high ceilings ,high colonial skirting boards ,china white paint and ornate conices , so the gaps in between the  boards look natural .
I also used Bona Traffic and the satin finish looks great with the gaps .But i do not think this would be the case with a hard gloss ... 
I just now wish i would have finished the garden Reno before it was done as the sand and Bona traffic do not go well together .  . 
Oh and don't let the misses ? or her friends wear worn down high heals on the floor .I now have what looks like the complete works of J.K rowlings (harry potter ) in braille in the kitchen floor  .
Lastly if you are not doing the floor  yourself P.M me and i will give you the names of the guys i used as i have got two different jarrah floors sanded and covered with Bonna Traffic and the results wear very different between the two different companies i used .
If you don't get somebody that knows what there doing you will get lines in it . 
best of luck rob

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## bcaso

Revival of an old thread. 
Has anyone ever used the glue that most people use  to hold the boards down "Bostic Ultraset" or the like, to fill in the gaps?  Similar colour to the boards and pretty flexible, won't re-open but may squeze out if boards expand (not sure). 
Just a thought! 
After typing this I thought the clear coat wouldn't work if waterbase finish was used???

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## m6sports

Dusty as always great Pics  :Hooray: 
i could look at them all day 
i just wish i had floors that nice at home

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## leeton

You're right m6, and I should have floors like that in a few weeks...I just booked Dusty for our place...hope he takes pics of ours and puts them on his web page. :Biggrin:

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## Dusty

Chit. Talk about under the pump. :Sweatdrop:   
Looking forward to it. :Smilie:

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## gbx78

those pics loook totally awesome.. now whats stopping me from doing my floors is i have a dog, she doesnt tend to do burnouts on the floor however im wondering how hard of a finish can you get to prevent or at least minimise scratches.. i have a small house and im tempted to just tile over for durability and less maintanence .. but god dammit .. i LOVE polished floors!!! mines not polished gloss mine apears to be a matt finish? perhaps even oiled, its very dull. Has lots of scratches dings marks stains and not even level in some places, hence why im tempted to nail down some villaboard and just tile over on a flat surface... :/

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## leeton

Well, I have had the man "Dusty" in to do my floors, and as expected...a top job.
Thanks mate. :2thumbsup:

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## Dusty

> Well, I have had the man "Dusty" in to do my floors, and as expected...a top job.
> Thanks mate.

  No problemo. All in a days..er, actually three days work.  
Thanks for the great hospitality. Toast, crumpets, coffee, fish n chips, dim sims. I think I've gained 2.5 kilo's in those three days.  :Smilie:

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## Simply Bamboo

Hello Guys 
You wouldn`t have this problem if you used pre-finished bamboo flooring.  Bamboo Flooring is the most stable plant on earth, so doesn`t move much of the year.  You would find that over years the floor will have no gaps.

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## glock40sw

> Hello Guys 
> You wouldn`t have this problem if you used pre-finished bamboo flooring. Bamboo Flooring is the most stable plant on earth, so doesn`t move much of the year. You would find that over years the floor will have no gaps.

  
Really?? 
I wonder why 80% of all floor problems are with Bamboo floors? 
Confirm this with ATFA if you like..

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## Dusty

> Really?? 
> I wonder why 80% of all floor problems are with Bamboo floors? 
> Confirm this with ATFA if you like..

  Funny you say this, Trev. From what I hear (and I've got my ear to the floor  :Smilie:  you're right on the money with that.  
In all seriousness, with the problems I'm hearing about a lot of it stems from how the Bamboo reacts to slab moisture and I think the more everyone learns about it the better off it will be across the board, over time.

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## drewm

> Really?? 
> I wonder why 80% of all floor problems are with Bamboo floors? 
> Confirm this with ATFA if you like..

  I have the stats from the ATFA in front of me atm.  *Inspections on Bamboo Floors 
2007...................................4
2008...................................12
2009...................................16
2010....................................5 (first 3 months only)* 
Now I am sure you will agree that these would not compromise 80% of all inspections done during those various years. 
Bamboo will never amount to 80% of all inspections as it is such a relatively small portion of the market atm. It can't be that the 80% figure is a percentage of all bamboo floors as otherwise there would be hundreds if not thousands of inspections per year and yet we are seeing relatively small numbers.  
The numbers are definitely increasing as more bamboo (and more lower grade bamboo) is imported but at first glance I would have to assume that you have pulled the 80% figure out of your @@@@. 
Dusty the problem is not how bamboo reacts with slab moisture but rather how prefinished products react with slab moisture. 
The standard slab releases a certain amount of moisture constantly over its life. 
A timber or bamboo unfinished allows this to pass through in sufficiient quantity to not affect product
A on site finish (whether solvent of water based) allows any amount of moisture to pass thru (as vapour) 
The standard aluminium oxide pre-finishes allow only a minimal amount to pass thru which can result in a build up in the board and cupping ot some of the other problems experienced. 
A single coat of a 2 part epoxy moisture barrier controls this but not enough to prevent it being an issue in all but the driest of slabs.
A single very thick coat or 2 normal coats controls the release of moisture from the slab sufficiently that there is no buildup in the boards. 
It also helps considerably if the boards are balanced to the ATFA recommended 10-12% rather than the factory standard 6-10% (with a 7-7.5% average) but this requires a serious manufacturer that knows what they are doing, asking for and that the factory have actual humidity controlled kilns rather than standard oven drying. 
This is an area where I am at least reasonably knowledgeable and do have reasonable interaction with the ATFA and direct interaction with factories in China during the course of my everyday work.

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## glock40sw

Well I was told that 80% is the number. 
So there ya go.

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## drewm

> Well I was told that 80% is the number. 
> So there ya go.

  It probably feels like it with the increasing amount of lower grade bamboo being brought in and the associated problems when lower grade products are sold as the "ducks nuts"  :Doh:

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