# Forum Home Renovation Decking  Is oiling of the underside of deck boards required?

## RobR

As the title says, do i need to oil the underside of the deckboards prior to screwing them down. I have conflicting info as to if this is needed or not so any info would be greatly appreciated. 
Rob

----------


## Bloss

Not necessary.

----------


## RobR

That's the answer I was looking for.  :Redface: )
Thanks

----------


## robinclohessy

> As the title says, do i need to oil the underside of the deckboards prior to screwing them down. I have conflicting info as to if this is needed or not so any info would be greatly appreciated. 
> Rob

  
yes.... if you want it to last... why do things half arsed..

----------


## jimj

I am probably half arsed on most things but I would 100% agree with Bloss on this question. Waste of both time &money spent on coating product. The greatest degrader of both horizontal timber is the sun's UV. I am yet to see the sun reach the underside of the timber.    :Biggrin:   
jimj  restore-a-deck.com.au

----------


## simopimo

By all means paint the underside but oil would be a waste. The paint can provide protection from moisture underneath.

----------


## Bloss

> yes.... if you want it to last... why do things half arsed..

  Gotta watch those old posts - reckon the OP has done his deck already - after 3.5mths  . . .

----------


## ringtail

> I am probably half arsed on most things but I would 100% agree with Bloss on this question. Waste of both time &money spent on coating product. The greatest degrader of both horizontal timber is the sun's UV. I am yet to see the sun reach the underside of the timber.     
> jimj  restore-a-deck.com.au

  
For what its worth, I agree 100 % too

----------


## Connollys

Oiling both sides of the boards can do no harm and only help to keep the decking stable.  :2thumbsup:

----------


## grantbudd

I checked out my decking boards yesterday as some bright spark installed the whole lot upside down with the grooves facing up!!!! Facing deck is splintered, cracked and rotten in places. Under the timber looks great but I will throw it and start again....I too was thinking about oiling both sides given the oil will keep the moisture content similar both sides and prevent any movement?? I know the boards are kiln dried maybe and I know nothing about decking timber??? 
any help about this?? 
I do like doing something as I am exposed to salt air here in QLD  :Redface: )

----------


## jimj

I inspected a deck in Caloundra that was 18 months old,Kwila,domeheaded nails and coated with a kerosine based stain. The client was distressed as she wanted a deck that was like all her friends with a flat & smooth surface. I think I was the 5th person she had called. You couldn't pull up all of the boards and just flip them as it was around a pool with a lot of custom cut curves & angles. The purple tinged stain looked like ##$## and the galvanised domeheads were standing up like happy little mushrooms snagging your feet. When you walked on this deck it creaked . 
When I asked how this project happened it was a case of a friends relative who was a builder looking for work. He had built a lot of decks in England. He did ask her which way she wanted the boards. She said she had no idea and that your the builder. He said he would put the ribs up as that is what we do in England.
He built a 56m2 deck,low to the ground in 2.5 days by himself with all nails shot in with a nail gun spitting every board in the process. Someone else slopped on the kerosine glop. 
I wasn't sure if it could be sanded smooth or if I even wanted to try. Took a piece of scrap home and hand sanded the grooves off with my rotex. I thought ( stupidly) yeah maybe I could fix this.
She was pretty happy I was going to try this
I punched all the nails and started sanding. The grooves with my 90 kg sander came off but took 3 times as many abrasive belts & dust to be bagged & carted away.
The really hard work came when I had to do all of hand sanding. Sanding off a length of 600mm on one board at home is a lot easier than an entire deck of grooves .  OK  Got the  entire deck sanded & stained. She was delighted as for me several things are permanently etched into my brain.
1. The amount of force I had to exert through my body to hand sand the grooves gave me a hernia that required surgery & 6 weeks off from work.
2.That I am never going to be so STUPID again . 
I have been to newly laid decks that have had the boards coated prior to laying. During the process of laying the top the  surface has been scratched,muddied and is just a mess where if you added the rest of the coats required the outcome will not look as nice.
From my observations the sun is the killer and that is on the top surface. Thinking that the oil is going to keep things in balance(whatever that is) might make us feel good but what about when it rains for a week and the deck is covered in puddles for 2 weeks. The undeside will be damp but can't have puddles on it. 
By all means coat if you want.  
jimj    www.restore-a-deck.com.au---Buderim QLD

----------


## Marc

> I wasn't sure if it could be sanded smooth or if I even wanted to try. Took a piece of scrap home and hand sanded the grooves off with my rotex. I thought ( stupidly) yeah maybe I could fix this.
> She was pretty happy I was going to try this
> I punched all the nails and started sanding. The grooves with my 90 kg sander came off but took 3 times as many abrasive belts & dust to be bagged & carted away.
> The really hard work came when I had to do all of hand sanding. Sanding off a length of 600mm on one board at home is a lot easier than an entire deck of grooves .  OK  Got the  entire deck sanded & stained. She was delighted as for me several things are permanently etched into my brain.
> 1. The amount of force I had to exert through my body to hand sand the grooves gave me a hernia that required surgery & 6 weeks off from work.
> 2.That I am never going to be so STUPID again . 
> I have been to newly laid decks that have had the boards coated prior to laying. During the process of laying the top the  surface has been scratched,muddied and is just a mess where if you added the rest of the coats required the outcome will not look as nice.
> From my observations the sun is the killer and that is on the top surface. Thinking that the oil is going to keep things in balance(whatever that is) might make us feel good but what about when it rains for a week and the deck is covered in puddles for 2 weeks. The undeside will be damp but can't have puddles on it. 
> By all means coat if you want.  
> jimj    www.restore-a-deck.com.au---Buderim QLD

  Hi Jim, when you say you sanded the grooves off with the machine, what did you do after by hand that was so hard? The edges? 
As for the topic of coating the underside, I have seen my share of rotted decks and the rotting is in the top side of the boards and in the top side of the joist.
However, if you compare to exposed wood in a boat for example, you will get no argument that the underside of a deck needs to be painted.  
Perhaps, the debate should be around what is the best protection for the floor boards on a deck. Clearly it is not oil. We use oil as a compromise because it looks nice and we can still see the wood. Best protection would be of course a coat of exterior primer and several coats of some marine grade floor paint, and the same goes for the underside.
Now if we use oil for the top side compromising the protection for looks, we could still do something for the underside. To use oil on the underside seems a bad choice since no one will recoat every year under the deck. 2 coat of exterior paint before laying the boards down would be a better choice.
Having said that, good luck painting bottom side without dripping paint on what will be the top side. And what about the edges? If you paint them you will see the paint from the top, if you dribble paint you will see the dribble. 
If anyone is game to add so much extra work, and wants to see the underside clean and painted, a couple of coats of water based exterior paint would probably do no harm. You would hate to see how much that would add to your quote if a carpenter does the job and not you.

----------


## Bloss

> Oiling both sides of the boards can do no harm and only help to keep the decking stable.

  But it does bugger all good either and costs time and money. "Stable"? Not sure what that means - poor timber which is prone to warping or twisting will not be much improved or improved at all by oiling on any side or all sides. The fixing and top finishing good quality decking will determine how it performs. The difference in the life or serviceability of any decking by oiling or coating the bottom (or sides for that matter other than what runs over the edge as it is being applied) is three fifths of five eighths of . . . . 
There are two main issues which affect the appearance and life of timber: UV damage from the sun and water damage. Protective coatings are designed to mitigate these two - ie: resist UV damage to the timber (and the coating itself breaks down and in doing so protects the underlying timber - that's a simplistic description but is in effect what is happening) and to stop water soaking into the timber. 
Funnily enough on decking sun exposure to UV varies by location and design (so a covered deck can last 100 years and more) with the sides and underside having no UV exposure, and gravity means that water runs off and we leave gaps and use slopes/ fall in the design so it does not pool on the decking. If the timber is treated then UV is the primary damaging agent - undersides don't get to see much sunlight. 
Of course there are exceptions for protecting from water/moisture (although not UV). For example in sea mist/spray exposed coastal areas or in high humidity tropical or very cold areas, and especially high decks where the exposure to moisture is consistent, then all round coating and continued maintenance would be standard. And if you want a better look for an underside that is visible then go right ahead. 
But that's not where most Australians live - even on the coast and fringes where around 80% of us live the average relative humidity levels are low, rainfall is too with a tendency towards large events and long intervening dry periods and sun exposure is high to extreme. 
So yes, if someone wishes to spend their own money and time coating all sides of a deck that's their choice, but they shouldn't do it thinking it will make any significant difference to the life of the deck (unless they are in one of those exceptions).

----------


## jimj

Thanks Marc, 
When I write I often find it difficult to explain as clearly as my brain is thinking(which isn't that clear as well)
The hand sanding is maybe not that clear of explanation. With every deck where my large walk behind sander can fit I use that first. However it can only get so close say maybe 150-300 mm to the sides of the deck. If it is going up to a wall at the end of a deck it will stop with about 100-150 mm that it can't sand. These areas have to be sanded off with another tool. I initiallt paid 2500.00 for a Lagler edger that had an extension that could go under railings tha were 100mm high. However attemptig to clean off the coatings with this tool I found it left too many swirls marks for my liking and I then had to take my orbital sander to smooth out these marks. Edgers are fairly heavy and run on small wheels. When you are moving the edger across the boards dfrom one to the next the wheels hit the gap,tilts and gouges the timber. It is like trying to use a big&heavy angle grinder to sand with. 
 Depending on the deck you have to sand around weird & wonderful decks that conform to the pool shape,there are various posts encountered along with a variety of glass & aluminium pool fencing.
Add the fact that the edgers have a fairly woeful dust extraction which I think is as important as the quality of the sander. If you don't get the dust out of the way besides it in your face,you can't see what you doing as the timber you are trying to sand off is covered in dust and your very ineffective as you are sanding over dust instead the coating-wood you are trying to remove. 
I didn't start out using dust extraction as I had never needed it before and thought the $ was ridiculous. The same thoughts were when I saw the cost of the Festool 150 Rotex orbital sander. However, I had tried to sand by hand with my 100mm Makita orbital,my Triton orbital on an angle grinder,my 75mm wide Hitachi belt sander and even a larger Ryobi angle grinder on a slow speed all of which would remove crap but did aa woeful job or couldn't cope with the pressure needed to get the crap off.
When I finally tried to Festool it was an amazing discovery as this sander can easily remove fairly rugged timber and yet sand up to the highest grit you want to go without swirl marks.Most of my deck sanding is with 40-80 grit but I have some festool 24 which is like the feeling of bitumen.
The grooves were all sanded with Klingspor 40 grit. Even when using a large sander there will always be some or many boards that sit lower and the coating will still be there after the large sander is finished. These areas also need to be cleaned out.
OK they are around 900.00 which for most folks way too much but the time & effort it will save you as well as how this sander will work in the future is amazing.
I have totally killed 2 of them and carry 3 with me to a job. To kill one is difficult and they are warrantied for 3 years. Most of mine have been back for repairs several times.
However it is not uncommon fpr me to hand sand 4-6 hours in a day with a lot of pressure required. 
As I mentioned the other vital parts are dust extraction. Just about any good vacuum will work. The critical thing is to make sue the dust is collected in a bag and seperated from the filters & motors. If not things will clog up fast.
Quality abrasives are essential but once you use them you would hard pressed to go back to cheap. 
I don't think the issue of coating underneath is that big of deal one way or another. There will be those that say yes and others say no.
I have painted the underneath of my decks as I think they look better than the  raw exposed bearers & joists. I picked a solid water based acyrlic exterior paint that was very close to the colour of the Flood Spa& Deck that I use on the top. When you are recoating the deck on top the stain will dribble underneath. It is virtually invisible with the stain on the solid paint. 
I always shudder when I arrive to a deck that has been painted solid white,light green,skyblue etc underneath as I have to explain to the client that there will be dribbles.
jimj

----------


## jimj

Bloss you have a much way with words than me. I totally agree with your summation.  I would put the extra$ & time straight into  the beer fridge. 
jimj    :Biggrin:

----------


## shauck

> Bloss you have a much way with words than me. I totally agree with your summation.  I would put the extra$ & time straight into  the beer fridge. 
> jimj

  and the spare time drinking it.

----------


## Marc

> Thanks Marc, 
> When I write I often find it difficult to explain as clearly as my brain is thinking(which isn't that clear as well)
> The hand sanding is maybe not that clear of explanation. With every deck where my large walk behind sander can fit I use that first. However it can only get so close say maybe 150-300 mm to the sides of the deck. If it is going up to a wall at the end of a deck it will stop with about 100-150 mm that it can't sand. These areas have to be sanded off with another tool. I initiallt paid 2500.00 for a Lagler edger that had an extension that could go under railings tha were 100mm high. However attemptig to clean off the coatings with this tool I found it left too many swirls marks for my liking and I then had to take my orbital sander to smooth out these marks. Edgers are fairly heavy and run on small wheels. When you are moving the edger across the boards dfrom one to the next the wheels hit the gap,tilts and gouges the timber. It is like trying to use a big&heavy angle grinder to sand with. 
>  Depending on the deck you have to sand around weird & wonderful decks that conform to the pool shape,there are various posts encountered along with a variety of glass & aluminium pool fencing.
> Add the fact that the edgers have a fairly woeful dust extraction which I think is as important as the quality of the sander. If you don't get the dust out of the way besides it in your face,you can't see what you doing as the timber you are trying to sand off is covered in dust and your very ineffective as you are sanding over dust instead the coating-wood you are trying to remove. 
> I didn't start out using dust extraction as I had never needed it before and thought the $ was ridiculous. The same thoughts were when I saw the cost of the Festool 150 Rotex orbital sander. However, I had tried to sand by hand with my 100mm Makita orbital,my Triton orbital on an angle grinder,my 75mm wide Hitachi belt sander and even a larger Ryobi angle grinder on a slow speed all of which would remove crap but did aa woeful job or couldn't cope with the pressure needed to get the crap off.
> When I finally tried to Festool it was an amazing discovery as this sander can easily remove fairly rugged timber and yet sand up to the highest grit you want to go without swirl marks.Most of my deck sanding is with 40-80 grit but I have some festool 24 which is like the feeling of bitumen.
> The grooves were all sanded with Klingspor 40 grit. Even when using a large sander there will always be some or many boards that sit lower and the coating will still be there after the large sander is finished. These areas also need to be cleaned out.
> OK they are around 900.00 which for most folks way too much but the time & effort it will save you as well as how this sander will work in the future is amazing.
> ...

  Getting grooves off a deck board with an orbital sander even the best one in the world must require a high degree of heroism. To do so kneeling down and under balusters and around post ... well ... I would only do it on a very small deck, say 1x1   :Biggrin:  
Did you recover from the hernia?

----------


## jimj

No way was that heroism. Just plain stupid. This lady was distraught over this decking project and I wasn't certain if it  was even possible to do but sorry for her.. Well it can be done but not by me again. One was enough. 
Recovered from the hernia. A day surgery job, 1500.00 out of pocket & 6 weeks off work. Nothing like learning the hard way! 
jimj   restore-a-deck.com.au

----------


## Marc

HEHE, this reminds me of a famous cartoonist from eons ago who had a series on "Anonymous heroes" 
He represented all sort of obscure jobs done in exaggerated appalling conditions. One was the lab technician who faced with lack of equipment, tested the urine samples as you do a wine test .....eeeehw  :Cry:

----------


## intertd6

In regards to sanding the reeding off decking, that would reduce the thickness of the boards by a few mm making the decking too thin and below the minimum allowable thickness. Coating with a durable sealer to the underside of decking in exposed locations will extend the life of the decking and is common on higher end projects, just like its good practice to seal the ends and joints of joists, rafters, beams, weatherboards, decking in similar locations and using capping over the top surfaces of exposed joists before fixing decking.
regards inter

----------


## jimj

Probably need to add to the list of dos & don'ts that don't put the grooves on top & don't shoot in the dome headed nails either! 
jimj

----------

